LONDON — Two leaders of a far-right, anti-Muslim group in Britain announced Tuesday that growing extremism in the organization’s ranks has led them to quit — a decision helped by a group founded by former Islamist radicals.

Tommy Robinson and Kevin Carroll said they were leaving the small but high-profile English Defence League, the group they founded in 2009.

The Quilliam Foundation, an anti-extremism think-tank founded by former Muslim jihadists, said it had helped facilitate the pair’s departure.

The League claims to be a peaceful opponent of radical Islam, but its opponents accuse it of racism and anti-Muslim prejudice. Its protests — which are usually met by large counter demonstrations — have often turned violent.

Mr. Robinson, whose real name is Stephen Lennon, has been arrested several times, once for entering the United States using false ID.

Mr. Robinson said in a statement that he acknowledged “the dangers of far-right extremism and the ongoing need to counter Islamist ideology not with violence but with better, democratic ideas.”

And he distanced himself from the behaviour of some EDL supporters, telling the BBC that “whilst I want to lead a revolution against Islamist ideology, I don’t want to lead a revolution against Muslims.”

He said that as the face of the EDL, he was tired of being associated with the group’s excesses — such as the supporter photographed sporting a tattoo of an exploding mosque.

“When some moron lifts up his top and he’s got the picture of a mosque saying ’boom’ and it’s all over the national newspapers — it’s me,” he said.

“It’s when I pick up my kids from school the parents are looking at me, judging me on that. And that’s not what I’ve stood for and my decision to do this is to be true to what I stand for.”

Quilliam co-founder Maajid Nawaz said the announcement was “a very proud moment” for his group.

“We have been able to show that Britain stands together against extremism regardless of political views and hope to continue supporting Tommy and Kevin in their journey to counter Islamism and neo-Nazi extremism,” he said.

Anti-racism campaign group Hope not hate said it was skeptical about the news.

In a statement, director Nick Lowles said, “EDL supporters have called for mosques to be burned, holy books to be destroyed, Muslims to be deported, they have cost us £10m in policing bills, brought disorder to our streets, and many, many more have been sentenced for acts of violence, gun possession, paedophilia and other crimes.”

He added, “There have been rumours throughout the day that the pair intend to set up a new anti-Islamist political movement devoid of the racism of the EDL. To us, this will just be EDL mark II.